On the Calculation of Diffusion Coefficients in Confined Fluids and Interfaces with an Application to the Liquid−Vapor Interface of Water

Liu, Pu; Harder, Edward; Berne, B. J.

doi:10.1021/jp0375057

Cited by 369 publications

(505 citation statements)

References 29 publications

(39 reference statements)

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“…Finally, a modified Einstein relation provides the local in-plane diffusion coefficient. 46 Plotting 〈∆r b(τ) 2 〉 {z} /4P(τ) vs τ results in a straight line with a slope equal to D || (z):…”

Section: Resultsmentioning

confidence: 99%

Effect of Surface Polarity on the Structure and Dynamics of Water in Nanoscale Confinement

et al. 2009

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We present a molecular dynamics simulation study of the structure and dynamics of water confined between silica surfaces using -cristobalite as a model template. We scale the surface Coulombic charges by means of a dimensionless number, k, ranging from 0 to 1, and thereby we can model systems ranging from hydrophobic apolar to hydrophilic, respectively. Both rotational and translational dynamics exhibit a nonmonotonic dependence on k characterized by a maximum in the in-plane diffusion coefficient, D || , at values between 0.6 and 0.8, and a minimum in the rotational relaxation time, τ R , at k ) 0.6. The slow dynamics observed in the proximity of the hydrophobic apolar surface are a consequence of -cristobalite templating an ice-like water layer. The fully hydrophilic surfaces (k ) 1.0), on the other hand, result in slow interfacial dynamics due to the presence of dense but disordered water that forms strong hydrogen bonds with surface silanol groups. Confinement also induces decoupling between translational and rotational dynamics, as evidenced by the fact that τ R attains values similar to that of the bulk, while D || is always lower than in the bulk. The decoupling is characterized by a more drastic reduction in the translational dynamics of water compared to rotational relaxation.

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Section: Resultsmentioning

confidence: 99%

Effect of Surface Polarity on the Structure and Dynamics of Water in Nanoscale Confinement

et al. 2009

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“…Instead, we developed a general methodology to evaluate the diffusion coefficients in an inhomogeneous liquid or a confined liquid. 40 The diffusion coefficient in the interface can be reduced to a component parallel to the surface D xx ) D yy ) 0.8 Å 2 /ps (f ) 2) and a component perpendicular to the surface D z ) 0.5 Å 2 /ps (f ) 1), 40 as seen in Figure 5. For the bulklike region, D xx ) D yy ) D zz ) 0.22 Å 2 /ps, which is similar to the experimental result of Conditional hydrogen-bond autocorrelation after eliminating the effect of diffusion for the bulk and the interface for the TIP4P/FQ water model.…”

Section: Resultsmentioning

confidence: 99%

Hydrogen-Bond Dynamics in the Air−Water Interface

2005

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Hydrogen-bond (H-bond) dynamics in the air-water interface is studied by molecular dynamics simulations. The analysis reveals that the dynamics of breaking and forming hydrogen bonds in the air-water interface is faster than that in bulk water for the polarizable water models. This is in contrast to the results found on a protein surface. We show that the difference stems from more rapid translational diffusion in the interface. When the effect of pair diffusion is eliminated, the hydrogen-bond dynamics in the interface is observed to be slower than that in the bulk. This occurs because the number of water molecules adjacent to a hydrogenbonded pair and available to accept or donate a hydrogen bond is smaller in the interface than in the bulk. The comparison between polarizable water models and fixed-charge models highlights the potential importance of the polarization effect in the water-vapor interface.

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“…26,32 The cut-off distances are 3.1, 3.5, 3.6, and 3.9 Å for sodium, potassium, chloride, and iodide, respectively. To find the diffusion constants in the various regions relative to the ions, we modified the method of Liu, Harder, and Berne, 39 developed for calculating diffusion constants near interfaces. The diffusion constants are found from the mean square displacements of the center-of-mass of the water molecules in region A.…”

Section: Methodsmentioning

confidence: 99%

The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions

Nguyen

Rick

2018

The Journal of Chemical Physics

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A relationship between the effect of uni-univalent electrolytes on the structure of water and on its volatility The Journal of Chemical Physics 148, 222807 (2018) The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions The diffusion rates for water molecules in salt solutions depend on the identity of the ions, as well as their concentration. Among the alkali metal ions, cesium and potassium increase and sodium strongly decreases the diffusion constant of water. The origin of the difference can be understood by examining the simulation results using different potential models. In this work, aqueous solutions of salts are simulated with a variety of models. Commonly used non-polarizable models, which otherwise reproduce many experimental properties, do not capture the trend in the diffusion constant, while models which include polarization and/or charge transfer interactions do. For the non-polarizable models, the diffusion constant decreases too strongly with salt concentration. The changes in the water diffusion constant with increasing salt concentration match the diffusion constant of the ion. The ion diffusion constant is dependent on the residence time for water in the ion solvation shell. The non-polarizable models over-estimate the residence time, relative to the translational diffusion constant and so tend to under-estimate the ion and water diffusion constants. Published by AIP Publishing.

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On the Calculation of Diffusion Coefficients in Confined Fluids and Interfaces with an Application to the Liquid−Vapor Interface of Water

Cited by 369 publications

References 29 publications

Effect of Surface Polarity on the Structure and Dynamics of Water in Nanoscale Confinement

Effect of Surface Polarity on the Structure and Dynamics of Water in Nanoscale Confinement

Hydrogen-Bond Dynamics in the Air−Water Interface

The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions

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